Different Types of Keys in DBMS
Keys in DBMS:
DBMS Keys are a data item that exclusively identifies a record.
Example: Account_number, Employee_number and customer_number is used as a DBMS Keys because they specifically identify a record stored in a database.
Types of Keys in DBMS:
There are six types of keys in DBMS are:
1. Super Key:
A Super key for an entity is a set of one or more attributes whose combined value uniquely identifies the entity in the entity set. Superset of any candidate key is also known as Super key.
2. Primary Key:
The primary key uniquely identifies each record in a table and must never be the same for two records.
3. Candidate Key:
A candidate key is an attribute or a set of attributes that it identifies a record uniquely. These attributes or combinations of attributes are called candidate keys.
Here, Two Candidate Keys are present in this table is given below:
4. Composite Key:
A composite key is a group of fields that it combines to uniquely identify a record. When we design a database, we will have tables that will use more than one column as a part of the primary key. So, it is called a composite key or concatenated key.
Here Two Composite Keys are present in this table is given below:
5. Foreign Key:
In relation, the column whose data values correspond to the values of a key column in another relation is called a Foreign Key.
Here, only one Foreign Key is present in both table is given below:
6. Secondary Key:
A secondary key is an attribute or combination of attributes that may not be a candidate key but classifies the entity set on a particular characteristic. A table can have multiple choices for a primary key but the only one can be set as the primary key. All the keys which are not the primary key that is called Secondary Key.
In this table, Student_id, Roll_no, email_id are qualified to become a primary key. But since Student_id is only the primary key. Here Two Secondary Keys are present in this table is given below: